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Pests resistant to GM crops: study

ELEANOR HALL: Scientists in the United States say they've have discovered how some insects become more resistant to some genetically-modified crops.

Since 1996, farmers worldwide have planted more than 400 million hectares of genetically modified corn and cotton.

Some scientists have been warning that the widespread use of the insecticide proteins in GM crops would lead to resistance in pests.

Now a team from the University of Arizona has analysed data from 77 studies to figure out why some insects become resistant quickly but others don't.

Professor Bruce Tabashnik led the research and he spoke to Alison Caldwell.

BRUCE TABASHNIK: Well in the worst cases that have happened the pests did become resistant very quickly in certain situations but there were other cases, including some great examples from Australia, where this resistance has been delayed for more than a decade.

ALISON CALDWELL: How have they managed to do that?

BRUCE TABASHNIK: The main strategy for delaying evolution of resistance in the pests is called the refuge strategy, and this involves making sure that these pests have some crops that they like to eat that don't produce the Bt proteins.

And by doing that we allow some of the susceptible insects to survive and that helps to delay the evolution of resistance.

ALISON CALDWELL: In reality does that mean having a crop nearby that doesn't have any of these GM plants in them?

BRUCE TABASHNIK: That's exactly right. So for example if a grower was planting Bt cotton it could be a non-Bt, that is a normal variety of cotton, one that doesn't make the Bt proteins, or it could be another crop that the same pest likes to eat, for example sorghum that also doesn't produce the Bt proteins.

ALISON CALDWELL: You still have a pest there in Arizona which is still resistant after all this time. What's the potential do you think?

BRUCE TABASHNIK: Still susceptible. So we have a pest in Arizona called the pink bollworm, and it's plagued cotton farmers in our state here for more than a century. But by using the Bt cotton with a very carefully orchestrated program that was developed in collaboration with farmers, industry and regulatory agencies, we found that this pest can be suppressed with the Bt cotton and resistance hasn't evolved despite its extensive exposure to cotton for more than 15 years.

As a contrast, in India, the same regulations or similar regulations were in place but the infrastructure wasn't there to get the high compliance from the farmers, and they didn't plant the refuges and the same insect quickly evolved resistance to Bt cotton there.

BRUCE TABASHNIK: Absolutely, because insects are champions at adapting. We expect them to adapt to whatever control method that we can think of. But if we're proactive and we coordinate our efforts, we think we can apply evolutionary principles to slow down their adaptation, to make environmentally friendly control methods like Bt proteins last longer.

ELEANOR HALL: That's Professor Bruce Tabashnik from the University of Arizona, speaking to Alison Caldwell. The study has been published in the journal Nature Biotechnology.